Microdisplacement rendering at an angle
Looks like you're using a nightly build of Blender with vector displacement support. In that case, you'll need to translate the map with the new "Displacement" (displace along normal) node. Add Node > Vector > Displacement. That node can also replace your math nodes if you like, use the "offset" value instead of the subtract node and the "scale" value instead of the multiply node. They do the same thing, just built-in functionality. Plug your displacement map itself into the "height" input.

See also: What value does the Displacement input of the Cycles Material Output node expect?